Touch probes of coordinate measuring machines provide points of contact with test objects for measuring a succession of points on the test objects generally referenced to the coordinate axes of the measuring machine. Typically, different points on a test surface of the test object are measured by relatively moving the probe with respect to the test object. The relative motion can be achieved by moving the probe, moving the test object, or both. Motions along or about the coordinate axes are typically measured to record positions of the probe at the different points of contact.
Coordinate measuring machines of this type can be fitted with mechanisms for retracting the probes when not in use. For example, the probes can be retracted to provide clearance for removing the test objects, for mounting new test objects, or for repositioning the probe to measure different portions of the same test objects. In addition, the probes can be retracted for performing other types of measurements, e.g., optical measurements, within a compound measuring machine, such as an optical imaging measuring machine combined with a coordinate measuring machine for collecting area data in addition to point-by-point data regarding the test objects.
An example of a retractable probe is described in U.S. Pat. No. 8,316,728 of Lawson et al., which is hereby incorporated by reference. A deployment mechanism for retracting and extending the probe includes a lead screw that moves the probe into and out of engagement with a kinematic mount. Although the kinematic mount is designed for positioning the probe, forces exerted by the retractor mechanism can prevent the probe from seating in exactly the same position each time it is deployed. Relatively small lateral forces acting over the length of the lead screw can produce an asymmetric distribution of forces at the kinematic mount, which can interfere with the accurate seating of the probe on the mount.